Among the 220,000 lower-limb amputees and about 60,000 new amputees/year in the U.S., many are dissatisfied with their prothesis. They endure constant pain and discomfort which they assume to be unavoidable. The comfort, energy efficiency, and security of a prosthesis are related directly to the fit of the socket. Yet, the consistent, precision fit of a socket has proven elusive because of natural fluctuations in the size of an amputee's residual limb. The result of chronic discomfort and an expensive, often never-ending, search for a more comfortable prosthesis. To correct this basic defect, we will innovate a Smart Variable-Geometry Socket (SVGS) for lower-limb prostheses. Phase I will demonstrate the feasibility of the main feature of SVGS -- a unitary, variable-volume bladder/sensor component. The bladder is filled with a responsive gel whose volume can be varied electrically. The pressure sensor provides feedback to an onboard microcomputer control. The result will be a socket that automatically compensates for volumetric variations of the residual limb. It will create a consistent and precise fit which should lower the need for, and cost of, continued rehabilitation and should improve greatly the quality of life for lower- limb amputees. PROPOSED COMMERCIAL APPLICATION This SBIR program will lead to a major improvement in lower-limb prostheses by providing an important new advantage -- a socket that will adjust automatically for diurnal and longer-term volumetric variations of the residual limb. Widespread utilization of SVGS is expected. We believe that will become the ubiquitous socket design for lower-limb amputees. A world-wide business of sever $10 millions should develop within five (5) years for the SVGS.